Urgent: Help needed on impedance matching in antenna

[sbhalerao]

Hi to all,
I am a part of a research group that is presently investigating the feasibility of powering sensor nodes.. Our work involves the design of an antenna and a rectifier circuit. The rectifier uses a Zero-biased Schottky diode (Agilent HSMS-2850)..
I am using IE3D for the antenna simulation (for the first time). I am going to connect the antenna directly to the rectifying circuit (without using any matching circuit).. this is to done to avoid bulky components. I have NOT been able to achieve impedance match till now..
The concept is that the impedance of the rectifier circuit should be equal to the impedance of the antenna..
1) ZL and Zc are given ... ZL corresponds to load and Zc is the characteristic impedance of the transmission line... Is load the antenna in my case and the Zc is the impedance of the rectifier circuit???
2) I have to specify ZL.. If it is the antenna impedance, how can I specify it ??? it should come up as Z11??

I understand the concepts, but the terms used in IE3D are not that clear to me... I would be glad if someone could enlighten me on this... The antenna that I am designing is a folded-patch antenna... I know all stuff about that - but this impedance matching business is driving me crazy!!!

 

[vfone]

Here I assume that is about a receiving antenna direct connected to an RF detector.
First of all, in your simulation beware about power levels on the detector.
The diode impedance is a function of power absorbed, so the diode impedance would change for different powers. A matching circuit would help for this problem, but I understand that you want to avoid this circuit.
I would recommend to simulate separate the impedance of the detector (e.g. using a non-linear simulator), and after that using IE3D, simulate the antenna and tune its ZL impedance to match to detector’s impedance.
In an un-matched detector, a DC return resistor in parallel to the ZL (500 to 1000ohms) would help to broaden the match, improving the VSWR and power loss.

 

[xxargs]

Here I assume that is about a receiving antenna direct connected to an RF detector.
First of all, in your simulation beware about power levels on the detector.
The diode impedance is a function of power absorbed, so the diode impedance would change for different powers. A matching circuit would help for this problem, but I understand that you want to avoid this circuit.
I would recommend to simulate separate the impedance of the detector (e.g. using a non-linear simulator), and after that using IE3D, simulate the antenna and tune its ZL impedance to match to detector’s impedance.
In an un-matched detector, a DC return resistor in parallel to the ZL (500 to 1000ohms) would help to broaden the match, improving the VSWR and power loss.

Is depend of used frequency, but i thinking orginal writer need some kind of band pass filter between antenna and rectifier.

naked rectifier directly connected to antenna is _not_ _good_ if want pass FFC and CE-approve before allow selling, ie. rectifier give much spurs and intermodulation product in high RF-field strength area as near any kind of radio base stations, TV and broadcast transmiter and, not forget, sending GSM-mobile (cell) phone...

ie. need design in band pass filter between antenna and rectifier, and in smart design also can use this as impedance transformer betweeen antenna and rectifier.

 

[sbhalerao]

Here I assume that is about a receiving antenna direct connected to an RF detector.
First of all, in your simulation beware about power levels on the detector.
The diode impedance is a function of power absorbed, so the diode impedance would change for different powers. A matching circuit would help for this problem, but I understand that you want to avoid this circuit.
I would recommend to simulate separate the impedance of the detector (e.g. using a non-linear simulator), and after that using IE3D, simulate the antenna and tune its ZL impedance to match to detector’s impedance.
In an un-matched detector, a DC return resistor in parallel to the ZL (500 to 1000ohms) would help to broaden the match, improving the VSWR and power loss.

Yeah, that's what we want to do !!! We want to connect the diode detector directly to the antenna.. i will do as you say... Tahnk you for your help..
Going by what you say, i will have to analyse the diode detector circuit impedance for various values of input power (I am using ADS for this purpose)
and then adjust ZL of the antenna accordingly in the IE3D simulation...

However, I don't understand how a Dc return resistor parallel to ZL would broaden the match??? Could you elaborate on this thing??

Thanking all who replied..
Shantanu Bhalerao.

 

[vfone]

Resistors could improve the VSWR in an unmatched circuit, at the cost of insertion loss.
But in the same time in an unmatched circuit you get loss of power due to mismatch loss Mismatch Loss (dB) = – 10*LOG (1 – Γ²)
Power loss due to reflections from an unmatched diode is up to 3dB worse than that due to the matching network using resistor.